Modern radar systems use solid-state devices because of their reliability. Solid-state devices are not only reliable, but operate at relatively low voltages by comparison with traditional vacuum tube devices, including such devices as magnetrons and klystrons. It is well known that radar systems, of whatever type, may require substantial transmitter power for generating electromagnetic signals capable of traversing the path between the transmitter and the target, being reflected, and returning to the radar system with sufficient amplitude to be detected in the presence of unavoidable system noise. Thus, the transmitter of a solid-state radar system may require substantial power at relatively low voltage.
Radar systems often operate in a pulse mode. Thus, a solid-state radar system may require pulsed power at relatively low voltage. The power supply for a radar transmitter is often a power source such as, for example, a constant-voltage source together with an inductance-capacitance (LC) filter or energy storage circuit which matches the pulse load with the average-power source.
In FIG. 1, a radar system 10 includes an antenna designated 12, coupled to a transmit/receive (T/R) device 14. A transmitter 16 and an analog receiver 18 are coupled to the transmit-receive device 14. Receiver 18 processes received reflected radar signals, and couples the processed analog signals to a digital processing arrangement illustrated as a block 20. A radar control computer (RCC) 22 is coupled to the transmitter 16, receiver 18, and to receive processor 20, for interacting with and synchronizing the various different portions of the radar system. A human interface illustrated as a block 24 represents controls for setting the various modes of operation of the radar, and for displaying radar information, as for example a plan-position indicator, all as well known in the radar arts. As illustrated in FIG. 1, a power supply (PS) 26 receives mains 28 power, and is connected for supplying power to the transmitter 16 and a capacitor C30.
FIG. 2 illustrates an equivalent circuit representing the prior-art transmitter 16 and its connections to the power supply 26. In FIG. 2, 3-phase, 480 volt power is applied from mains 28 to the power supply 26. Power supply 26 is a constant-voltage supply, which may be energized from either and alternating-current (AC) or direct-current (DC) source. As illustrated, the output of power supply 26 is 32 volts direct (also known as direct current or DC) at an output node, port or terminal 2601 relative to return node, port or terminal 2602. Return terminal 2602 is connected to the ground of transmitter 16, represented by conventional ground symbols, some of which are designated 16i2.
In FIG. 2, output terminal 2601 of power supply 26 is connected by an energy storage filter 210 to transmitter circuit 16. Energy storage filter 210 includes an inductor 2102 connected in “series” between power supply output terminal 2601 and transmitter input power node 16i1. A capacitor CM is connected between transmitter input power nodes 16i1 and 16i2.
It should be noted that the terms “between,” “across,” and other terms such as “parallel” have meanings in an electrical context which differ from their meanings in the field of mechanics or in ordinary parlance. More particularly, the term “between” in the context of signal or electrical flow relating to two separate devices, apparatuses or entities does not relate to physical location, but instead refers to the identities of the source and destination of the flow. Thus, flow of signal “between” A and B refers to source and destination, and the flow itself may be by way of a path which is nowhere physically located between the locations of A and B. The term “between” can also define the end points of the electrical field extending “across” or to points of differing voltage or potential, and the electrical conductors making the connection need not necessarily lie physically between the terminals of the source. Similarly, the term “parallel” in an electrical context can mean, for digital signals, the simultaneous generation on separate signal or conductive paths of plural individual signals, which taken together constitute the entire signal. For the case of current, the term “parallel” means that the flow of a current is divided to flow in a plurality of separated conductors, all of which are physically connected together at disparate, spatially separated locations, so that the current travels from one such location to the other by plural paths, which need not be physically parallel.
In addition, discussions of circuits necessarily describe one element at a time, as language is understood in serial time. Consequently, a description of two interconnected elements may describe them as being in “series” or in “parallel,” which will be true for the two elements described. However, further description of the circuit may implicate other interconnected devices, which when connected to the first two devices may result in current flows which contradict the “series” or “parallel” description of the original two devices. This is an unfortunate result of the limitations of language, and all descriptions herein should be understood in that context.
The term “coupled” as used herein includes electrical activity extending from one element to another element either by way of an intermediary element or in the absence of any intermediary element.
In FIG. 2, the transmitter 16 can be seen to be made up of a plurality of mutually-parallel-connected “modules” of a set 220 of modules. More particularly, set 220 of modules includes six modules designated 2201, 2202, 2203, 2204, 2205, and 2206. These modules are identical, so that a description of one suffices to explain all. All the modules of set 220 are electrically connected to energy storage filter 210 by way of a conductive bus designated 219 and the various ground connections 16i2. The combined capacitances of capacitor CM of FIG. 2 together with the capacitances of the various capacitors C of the modules 2201, 2202, . . . 2206 of set 220 of modules make up capacitance C30 of FIG. 1.
Taking module 2203 as being representative of any of the modules of set 220, each module of set 220 includes a capacitor paralleled by a resistor and also paralleled by a switched resistance. Thus, module 2203 includes a load resistance 22031 in series with a switching element 22032, which is illustrated as being a field-effect transistor (FET), to thereby constitute the switched resistance 22052 The conductive state of the FET is controlled by a “strobe” (STYM) pulse signal applied from the RCC 22 of FIG. 1. The switched resistance 22052 is connected between bus 219 and the transmitter 16 ground 16i2. A capacitor 22033 is also coupled between bus 219 and the transmitter 16 ground 16i2, so the capacitor is in parallel with the switched resistance 22052. A further resistance in the form of a resistor 22034 is also coupled between bus 219 and the transmitter 16 ground 16i2, so the resistor 22034 is in parallel with the capacitor 22033 and switched resistance 22052.
As illustrated in FIG. 2, the value of inductor 2102 is 2.5 milliHenry (mH), and the value of capacitor 210C is 230 Farads (F). Resistor 22034 of module 2203, and other corresponding resistors, is or are continuously connected across bus 219 (between bus 219 and ground). The bus voltage is 32 volts direct (32 VDC), and the current 22035 flowing through resistor 22034 is indicated as being 5 amperes (A). Thus, resistor 22034 and the other corresponding resistors each have a value of about 6.4 ohms. The values of resistors corresponding to resistor 22031 is or are about 0.45 ohms.
Inductor 2102 of FIG. 2 provides an inductance of 2.5 milliHenries at an average current of many hundreds of amperes. This inductor can be as large as an office cabinet and weigh tons, and is very costly. If it should fail, replacement with a spare unit is clumsy and time-consuming. Improved radar systems and power arrangements are desired.